The twins from Colby, Kan., first visited the Walnut Valley Festival in utero. That was back in 1986, when their pregnant mother, Susan, and father, Bob, came here for the first time.

Born a few months later, Blake and Brandon, and their parents, have missed only one festival since then. Now the younger McLemores are part of what draws other bluegrass fans to the festival, as part of a band called Driven. They’re among dozens of acts who will perform during the five-day festival that officially gets under way Wednesday, including John McCutcheon, Beppe Gambetta, Steel Wheels, the Grascals, Marley’s Ghost and the Byron Berline Band.

The festival typically draws about 13,000 to 14,000 people, more than doubling the population of the town about 45 miles southeast of Wichita. In addition to 30 bands, the festival offers a juried arts and crafts show featuring nearly 100 exhibitors, 20 food vendors, workshops on autoharps, fiddling, songwriting and mountain dulcimers, and eight national or international contests, including the National Flatpicking Championships.

People began lining up for the festival in late August and were admitted to the Winfield Fairgrounds on Thursday during the annual land rush for the prime camping spots along the Walnut River.

Driven was invited to play on the festival’s Stage One, after a well-received performance last year.

“We were completely shocked at how well the crowd responded,” Blake, who plays the bass, said. “Our first show on Stage One, we had near a full house. The stands seat nearly a thousand people. We were completely humbled by that. We weren’t expecting half that to show up.”

Then again, by the time Driven took the stage, a good percentage of festivalgoers had probably already heard them play in one of the hundreds of campsite jam sessions that go on around the clock here. The McLemores grew up surrounded by music in Colby – their parents both play and sponsor a bluegrass festival there – but Winfield has always exerted a special pull on them.

“It’s just the atmosphere,” Blake said. “You might see these people once a year, but it’s like a big family reunion.”

Driven actually started coalescing at another festival, held in Lawrence, when they met banjo player Jimmy Campbell. Not long after, they hooked up with Jake Workman, who’d traveled from Utah to take part in the Walnut Valley Festival’s guitar contest.

“His experience that first year wasn’t as good as he anticipated,” Blake said. “He didn’t have much of a jamming experience. He was to the point where he wasn’t going to come back the next year, but we had ourselves a really good jam that night, and we just became really good friends.”

Jake’s wife, Rebekah, plays fiddle in Driven. All five members sing.

“We’ve had some people describe our sound as walking this really fine line of staying traditional enough that’s it still bluegrass, but the sound is so much more modern,” Blake said. “We really focus on our rhythm. Between the guitar, bass and mandolin chop, we really strive for a solid rhythm.”

The band’s first CD consisted of covers of traditional bluegrass tunes. At last year’s festival, members promised fans they’d have a new CD of original songs ready when they returned. However, by early February, they didn’t have a single song finished.

That’s when Brandon got busy, writing nine songs for the CD to go with other contributions by his bandmates.

“I wanted to find stories to tell, not just sing the same old things,” said Brandon, who plays the mandolin.

One song, called “The Old Man & Me,” tells of a young boy who becomes friends with an old farmer. “John 6” is a gospel-tinged a cappella number. The title track, “You’ll Be Lonely, I’ll Be Gone,” tells the story of a woman who drags her feet when it comes to marriage.

One thing Driven can’t be called is overexposed. Since playing its first show in 2009, Driven has performed about a half-dozen times most years, mainly because all the members have full-time jobs. But Blake said that could change depending on how the new CD is received.

In addition to playing at the Walnut Valley Festival, Driven will perform at 4 p.m. Sunday at Bartlett Arboretum in Belle Plaine.

“Some offers have come our way to really push ourselves more,” Blake said. “We just have to decide if we want to. We’ll have a powwow about it at the festival.”